PRINCIPLES OF ANTIMICROBIAL THERAPY

ANTIMICROBIAL THERAPY TAKES ADVANTAGE OF BIOCHEMICAL DIFFERENCES BETWEEN MICRO ORGANISMS AND HUMANS.

SELECTIVE TOXICITY RELATIVE RATHER THAN

ABSOLUTE.

PRINCIPLES OF ANTIMICROBIAL THERAPY

SELECTION OF ANTIMICROBIAL AGENT

- Identity of organism & its sensitivity - Site of infection- Safety of agent- Patient factors- Cost of therapy

Identity of organism Obtain sample prior to starting

therapy Microsopic examination Gram stain Culture media sensitivity

Site of infection The blood brain barrier Choose drugs which are more lipid

soluble Low degree of protein binding Low molecular weight

Safety of the agent Penicillins are among the least

toxic of the antibiotics Drugs such as chloramphenicol are

reserved for severe resistant cases

Patient factors All conditions which can ,< immune

function have to be looked for Alcoholism, DM, malnutrition,

advanced age, HIV. Renal function– drugs which are

nephrotoxic are to be avoided Pregnancy Lactation Drugs like tetracyclines,

aminoglycosides are to be avoided. Age new born –avoid chloramphenicol ,

infants--tetracycline

Emperic therapy prior to organism identification

Acutely ill patient Identification & sensitivity of organism

Selection of drug --Status of the patient- renal, hepatic.Pregnancy & lactation, age

-

-Bacteriostatic-Bactericidal

SpectrumNarrow spectrum-- IsoniazidExtended spectrum-- ampicillinBroad spectrum– tetracycline,

chloramphenicol

Minimum inhibitory concentration (MIC)

LOWEST concentration of the antibiotic which inhibits growth

To provide effective antimicrobial therapy the antibiotic concentration should be more than MIC

Minimum bactericidal concentration Lowest concentration of

antimicrobial agent that results in a 99.999 percent decline in colony count.

Combination of drugs used inMixed infectionsUnknown originResistant organisms Better to use bacteriostatic with

bacteriostatic, or bactericidal with bactericidal!

Synergism between the actions of two or more drugs. Two bactericidal agents: Use a penicillin and an aminoglycoside. The increase in cell-wall permeability caused by the penicillin allows for easier access of the aminoglycoside.

To delay development of resistance. For the treatment of "mixed" infections.

Drug resistance

Mainly byMutations of DNADNA transfer of drug resistanceModification of target sitesDecreased accumulationEnzymic inactivation

Complications of antibiotic therapyHypersensitivity--- penicillin-urticaria, anaph

shokDirect toxicity---- aminoglycosideSuper infections SUPERINFECTIONS: Oral, GU, and GI

superinfections can occur with use of antibiotics. GI infections are most common. Intestinal Candidiasis: Fungal overgrowth

of the Candida secondary to giving an oral antibiotic and depleting intestinal flora. Add an antifungal drug to treat it.

Staphylococcal Enterocolitis: Life-threatening infection with Staph Aureus as a result of antibiotics. To treat it: Stop the original antibiotic therapy. Start therapy with vancomycin or some other appropriate agent to fight Staph Aureus.

Pseudomembranous Colitis: Life-threatening infection of Clostridium Difficile secondary to antibiotic therapy. Stop the original antibiotic therapy.

Start therapy with vancomycin and/or metronidazole

Prophylactic antibiotics

prevention of streptococcal infections in patients with history of RHD

Prevention of TB in close relatives of patient

Prior to surgical procedures Prevent transmission of hiv from

mother to fetus.

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